ASAP4b is a genetically encoded fluorescent voltage indicator. It was generated by mutagenesis of ASAP2f and contains amino acid replacements L146G, S147T, S150D, H151G, F413G and R414Q compared to ASAP2f (PMID:37429962). For detailed kinetic and spectral properties and a comparison of ASAP4b with other fluorescent voltage indicators, see PMID:37429962.